In addition, a protocol to study factors in failed human peripheral nerve regeneration has now been set up and approved by the NINCDS Human Research Subpanel. This is Protocol No. 80-N-06. The first patient candidates are now being reviewed to determine their acceptability for this protocol. The cellular, biological and immunological factors in peripheral nerve regeneration are being studied in a rat vein-graft model. The vein graft serves as a chamber into which various biological agents such as collagen or "trophic" factor such as nerve growth factor as well as specific cell types grown in tissue culture can be added to study their effects on axonal regeneration. Quantitative light and electron microscopic measures are being utilized to analyze the effects. To date, human tumor cells in the vein graft have enhanced regeneration whereas microcrystalline collagen has inhibited the process. The influence of fetal dorsal root ganglion cells, cerebellar cells, cortical cells, and fibroblasts are currently under study.